"Trims Gone Wild".... Any ieas?

[MMGT1]

Attached is a log and tune of what has happened. Look at the scan and go to the 7 min and 5 seconds (frame 3815) mark, you'll see what I'm talking about pretty quick here.
The fuel trims go insane and if I dont "two-foot" the gas and brake it will stall. Any ideas that you guys might see??

Attachment 26599

Attachment 26600

I have been chasing this for two weeks now. Ive installed new harnesses to the MAF, IAT, and the Crank Position Sensor at the back of the motor. Replaced the MAF and the problem seems worse! If anyone has an idea....

As always guys... thanks for looking!!

[danthurs]

Looking over the scan, it looks like your engine temp hit about 176* and you went rich, so the LTFT started to pull fuel. Makes me think you have a vacuum leak. Because it seems to be temp related, I would check the EGR. Set the open temp for it higher and see if the problem goes away.

[MMGT1]

The car does not have an egr Dan. Enable temp is maxed for it. Here is all I have on this:

Couple of weeks ago I'm in the highway going to work and trims do exactly what you are seeing in the scan above. Got a MAF from the wrecker and installed it yesterday. Now the car is doing this at city speeds. After I posted this, I re-installed the old MAF and the car is not doing this at city speeds. I am betting if I take it on the highway right now it's going to do this at highway speeds. I have tried the "brake parts cleaner" everywhere to try and find a vac leak to no avail. I am going to have a smoke and then take it on the highway for a run with my old MAF back in and see if it is now happening at those speeds.

[danthurs]

OK, that blows that theory. Have you made any changes to the MAF curve? How about the PE tables? One thing I noticed is the O2s. Check to make sure you don't have a spark plug wire touching the O2 sensor wire. had a car here the other week that had funny readings. His plug wires were laying on the sensor wires. That helped but the problem turned out being a pigtail extension for the O2 sensor. Replaced that and the O2s settled down and the LTFT wasn't way off.

[MMGT1]

Attachment 26601

Changed the MAF to my old one and it is still doing the same thing. I had noticed that the O2 would go flat, and the trims would go insane. I have a 99 Grand Am as well that I know has a good MAF. I am going to take it and try it in this one to see if there is any change...
In the scan in this post acts up at 2:26 or frame 1227 if your looking. Ill post a scan of the MAF I'm taking from the '99 as soon as I'm back.

[danthurs]

I think the problem is the O2 because it flat lines. Had another car here a while back and had funny readings on the O2, turned out to be a broken wire band. It would move and stop working. If you unplug the O2 it should read about 450. How old is the sensor?

[MMGT1]

I was thinking the same thing with the sensor, so I bought a new one. This time the GM one from the dealer to make sure it was right. Sensor has been in the car for less than an hour of run time so far.
You did mention something that made me wonder though... the MAF table. I put it back to stock, trims are gone off by around 10% but the car did not do "it" when I just drove it around the block a couple of times. Like I said, trims are horribe but not doing what we saw there. I am going to give it a highway run and see if it goes crazy again.... Ill post up the scan

[danthurs]

If the O2 readings look better, but the LTFT is off a bit, you can make adjustments to the MAF curve to bring you in to the +5 to -5 range.

[MMGT1]

Attachment 26604

There is the highway scan with the stock MAF table back in. Idle in gear looks OK actually but at cruse and under load is where its way off. I am now wondering if I should be going back to looking for a vac leak! This one's got me .... lol

[danthurs]

See, now your O2s look way better. Your LTFT isn't all that bad, for the most part your running rich so it's pulling between 5 and 10%, could use a little work, but all in all, not that bad.

[MMGT1]

I think we got it man! I left the idle region alone in the MAF table, just adjusted the 4K to 7.5K region of the table. Its within 2% on the first try and I'm going to leave it there for now and see how it does. Spent quite a bit of time on the highway and for now it seems to be holding just fine! When "you" mentioned the MAF table earlier I remembered Russ saying not to mess with the idle region of the Maf on the v-6's... sure looks like it was the cause.... thanks for your input today man, much appreciated!!

[danthurs]

Any time

[MMGT1]

Just an update.... three days of highway driving and no sign of that "issue" anymore! Man, sure am glad to have it back on the road.